The present invention relates to the improvements of an intake-air quantity control apparatus for an internal combustion engine equipped with a variable valve timing system which electronically arbitrarily controls a quantity of intake air drawn into the engine closer to a desired value by way of valve timing control.
In recent years, there have been proposed and developed various electronically-controlled variable valve timing systems which can operate intake and exhaust valves electromagnetically or hydraulically to adjust an intake-air quantity by way of -valve timing control. One such electronically-controlled variable valve timing system having electromagnetically-driven valve units has been disclosed in Japanese Patent Provisional Publication Nos. 8-200025 and 11-311135. In the Japanese Patent Provisional Publication Nos. 8-200025 and 11-311135, engine valves are electronically controlled by means of an electromagnetic solenoid valve controller, instead of a typical cam-drive mechanism. On the other hand, an electronically-controlled, hydraulically-operated variable valve timing system has been disclosed in Japanese Patent Provisional Publication No. 5-71370. In case of the aforementioned electromagnetically-operated engine valve, the engine valve is electronically arbitrarily controlled by means of the electromagnetic valve controller and thus the valve timing can be controlled continuously over a very wide range. Generally, such an electromagnetically-powered engine valve includes a pair of electromagnetic coils respectively attracting an engine valve when the pair of electromagnetic coils are energized, and a pair of return springs biasing the engine valve respectively in a direction opening and closing of the engine valve. When an electromagnetically-powered valve is applied to an intake valve, it is possible to control a quantity of intake air while introducing intake air of a substantially atmospheric pressure level into the engine cylinder, by advancing an intake valve closure timing. By way of the intake-valve-closure-timing (IVC) advancement control, a pumping loss can be reduced, thus improving fuel economy.
However, in case of an electromagnetically-powered intake valve, there is a problem of a limited driving speed of the electromagnetically-driven intake valve. That is to say, in the case that the intake valve is driven by way of an electromagnetic force, the driving speed of the intake valve is generally kept at a specified speed regardless of engine speeds. The specified speed is determined depending on both the spring stiffness of each spring and the magnitude of inertial mass of movable component parts of the electromagnetically-powered valve operating device. Owing to the previously-noted limitation on driving speed, an engine operating range in which an actual intake-air quantity cannot be brought closer to a desired value by only the intake valve closure timing control, exists. When changing from one of an intake valve closed state and an intake valve open state to the other, the electromagnetically-powered valve operating device requires a specified operating time, regardless of engine speeds. In other words, the minimum operating time of the electromagnetically-powered valve operating device is also limited. For the reasons set forth above, the minimum working angle of the intake valve tends to become greater at high engine speeds. Therefore, it is difficult to bring the actual intake-air quantity closer to the desired value by way of only the valve timing control made to the electromagnetically-driven intake valve, in a high-speed, low-load operating range in which a desired intake-air quantity is comparatively small.
Accordingly, it is an object of the invention to provide an intake-air quantity control apparatus for an internal combustion engine, which avoids the aforementioned disadvantages.
It is another object of the invention to provide an intake-air quantity control apparatus for an internal combustion engine, which can control an intake-air quantity over a wide operating range by way of valve timing control of an electromagnetically-driven intake valve, irrespective of a limited driving speed of the intake valve, that is, limitations in the valve timing control.
It is a further object of the invention to provide an intake-air quantity control apparatus for an internal combustion engine, which can ensure smooth switching operation without any torque difference during switching between an operating range in which an actual intake-air quantity can be controlled closer to a desired value by valve timing control and an operating range in which the actual intake-air quantity cannot be controlled closer to the desired value by only the valve timing control.
It is a still further object of the invention to provide an intake-air quantity control apparatus for an internal combustion engine, which can maximize an IVC advancement control area in which a quantity of intake air can be controlled while introducing intake air of a substantially atmospheric pressure level into the engine cylinder, by advancing an intake valve closure timing, thus ensuring a reduced pumping loss and improved fuel economy.
In order to accomplish the aforementioned and other objects of the present invention, an intake-air quantity control apparatus for an internal combustion engine comprises a variable valve timing system associated with at least an intake valve, a throttle valve located upstream of the intake valve, a throttle actuator variably adjusting a throttle opening of the throttle valve, sensors detecting engine operating conditions, and a control unit configured to be connected electrically to the sensors, the variable valve timing system, and the throttle actuator, for automatically controlling an intake-air quantity of air entering the engine depending on the engine operating conditions, the control unit comprising a data processing section programmed to perform the following, calculating a desired intake-air quantity based on the engine operating conditions, calculating a first intake valve timing corresponding to the desired intake-air quantity, determining, responsively to the engine operating conditions, whether the desired intake-air quantity is below a threshold limit value that corresponds to a lower limit intake-air quantity above which valve timing control of the intake valve enables the intake-air quantity of the engine to be brought closer to the desired intake-air quantity, calculating a second intake valve timing substantially corresponding to the threshold limit value, setting a desired valve timing of the intake valve to the second intake valve timing when the desired intake-air quantity is below the threshold limit value, and calculating a desired throttle opening that realizes the desired intake-air quantity by throttle opening control of the throttle valve when the desired intake-air quantity is below the threshold limit value.
According to another aspect of the invention, an intake-air quantity control apparatus for an internal combustion engine comprises a variable valve timing system associated with at least an intake valve, a throttle valve located upstream of the intake valve, a throttle actuator variably adjusting a throttle opening of the throttle valve, sensors detecting engine operating conditions, and a control unit configured to be connected electrically to the sensors, the variable valve timing system, and the throttle actuator, for automatically controlling an intake-air quantity of air entering the engine depending on the engine operating conditions, the control unit calculating a desired intake-air quantity based on the engine operating conditions, and performing a first operating mode when the desired intake-air quantity is above a threshold limit value that corresponds to a lower limit intake-air quantity above which valve timing control of the intake valve enables the intake-air quantity of the engine to be brought closer to the desired intake-air quantity, and performing a second operating mode when the desired intake-air quantity is below the threshold limit value, the first operating mode in which the intake-air quantity of the engine is brought closer to the desired intake-air quantity by the valve timing control of the intake valve and a throttle opening area of the throttle valve decreases with a decrease in the desired intake-air quantity to realize a desired boost, and the second operating mode in which the intake-air quantity is brought closer to the desired intake-air quantity by reducing the throttle opening area of the throttle valve to below the throttle opening area of the first operating mode that realizes the desired boost.
According to a further aspect of the invention, an intake-air quantity control apparatus for an internal combustion engine comprises a variable valve timing system associated with at least an intake valve, a throttle valve located upstream of the intake valve, a throttle actuator variably adjusting a throttle opening of the throttle valve, sensors detecting engine operating conditions including at least engine speed, and a control unit configured to be connected electrically to the sensors, the variable valve timing system, and the throttle actuator, for automatically controlling an intake-air quantity of air entering the engine depending on the engine operating conditions, the control unit calculating a desired intake-air quantity based on the engine operating conditions, and calculating a threshold limit value that corresponds to a lower limit intake-air quantity above which intake valve closure timing control of the intake valve enables the intake-air quantity of the engine to be brought closer to the desired intake-air quantity, and variably controlling an intake valve closure timing responsively to the desired intake-air quantity so that the intake-air quantity is brought closer to the desired intake-air quantity by the intake valve closure timing control and decreasingly compensating for a desired throttle opening of the throttle valve with a decrease in the desired intake-air quantity in accordance with a first characteristic to attain a desired boost in a first operating range in which the desired intake-air quantity is above the threshold limit value, and variably controlling the intake valve closure timing toward a valve timing corresponding to a minimum working angle which is preprogrammed to be suitable for the engine speed and decreasingly compensating for the desired throttle opening with a decrease in the desired intake-air quantity in accordance with a second characteristic in a second operating range in which the desired intake-air quantity is below the threshold limit value, the first characteristic being a monotonic function according to which the desired throttle opening decreases with a decrease in the desired intake-air quantity, and the second characteristic being a predetermined characteristic curve according to which points lying on the predetermined characteristic curve are lower than points lying on the first characteristic within the second operating range.
According to a still further aspect of the invention, an intake-air quantity control apparatus for an internal combustion engine comprises a variable valve timing system associated with at least an intake valve, a throttle valve located upstream of the intake valve, a throttle actuator variably adjusting a throttle opening of the throttle valve, sensors detecting engine operating conditions including at least engine speed, and a control unit configured to be connected electrically to the sensors, the variable valve timing system, and the throttle actuator, for automatically controlling an intake-air quantity of air entering the engine depending on the engine operating conditions, and calculating a desired intake-air quantity based on the engine operating conditions and calculating a threshold limit value that corresponds to a lower limit intake-air quantity above which intake valve closure timing control of the intake valve enables the intake-air quantity of the engine to be brought closer to the desired intake-air quantity, the control unit comprising an intake-valve closure timing control means connected to the variable valve timing control system for variably controlling an intake valve closure timing responsively to the desired intake-air quantity so that the intake-air quantity is brought closer to the desired intake-air quantity by the intake valve closure timing control in a first operating range in which the desired intake-air quantity is above the threshold limit value, and for variably controlling the intake valve closure timing toward a valve timing corresponding to a minimum working angle which is preprogrammed to be suitable for the engine speed in a second operating range in which the desired intake-air quantity is above the threshold limit value, and a throttle control means connected to the throttle actuator for decreasingly compensating for a desired throttle opening of the throttle valve with a decrease in the desired intake-air quantity in accordance with a first characteristic to attain a desired boost in the first operating range, and for decreasingly compensating for the desired throttle opening with a decrease in the desired intake-air quantity in accordance with a second characteristic in the second operating range, the first characteristic being a monotonic function according to which the desired throttle opening decreases with a decrease in the desired intake-air quantity, and the second characteristic being a predetermined characteristic curve according to which points lying on the predetermined characteristic curve are lower than points lying on the first characteristic within the second operating range.
According to another aspect of the invention, an electronic control method for an internal combustion engine comprising a variable valve timing system associated with at least an intake valve, a throttle valve located upstream of the intake valve, a throttle actuator variably adjusting a throttle opening of the throttle valve, and sensors detecting engine operating conditions including at least engine speed, the electronic control method comprises calculating a desired intake-air quantity based on the engine operating conditions, calculating a threshold limit value that corresponds to a lower limit intake-air quantity above which intake valve closure timing control of the intake valve enables an intake-air quantity of air entering the engine to be brought closer to the desired intake-air quantity, comparing the desired intake-air quantity to the threshold limit value, retrieving an intake valve closure timing from a first desired intake-air quantity versus intake valve closure timing characteristic according to which the intake-air quantity is brought closer to the desired intake-air quantity by the intake valve closure timing control in a first operating range in which the desired intake-air quantity is above the threshold limit value, retrieving the intake valve closure timing from a second engine speed versus intake valve closure timing characteristic according to which the intake valve closure timing is set at a valve timing corresponding to a minimum working angle which is preprogrammed to be suitable for the engine speed in a second operating range in which the desired intake-air quantity is below the threshold limit value, decreasingly compensating for a desired throttle opening of the throttle valve with a decrease in the desired intake-air quantity in accordance with a first desired intake-air quantity versus throttle opening area characteristic to attain a desired boost in the first operating range, the first desired intake-air quantity versus throttle opening area characteristic being a monotonic function according to which the desired throttle opening decreases with a decrease in the desired intake-air quantity, and decreasingly compensating for the desired throttle opening with a decrease in the desired intake-air quantity in accordance with a second desired intake-air quantity versus throttle opening area characteristic in the second operating range, the second characteristic being a predetermined characteristic curve according to which points lying on the predetermined characteristic curve are lower than points lying on the first desired intake-air quantity versus throttle opening area characteristic within the second operating range.